Method and apparatus for transmitting ack/nack signal in wireless communication system

ABSTRACT

The present invention relates to a method and apparatus for transmitting an acknowledgement/not-acknowledgement (ACK/NACK) signal in a wireless communication system. The method includes the steps of: receiving a transmission block; and transmitting an ACK/NACK signal for the transmission block in a first subframe or a second subframe according to the size of the transmission block, wherein, when the size of the transmission block is smaller than or equal to a reference value, the ACK/NACK signal is transmitted in the first frame, when the size of the transmission block is greater than the reference value, the ACK/NACK signal is transmitted in the second subframe, and the second subframe is behind the first subframe in a time domain.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method and an apparatus for transmitting areception acknowledgment for a hybrid automatic repeat request of a userequipment in a wireless communication system.

Related Art

3^(rd) generation partnership project (3GPP) long term evolution (LTE)(hereinafter, referred to as LTE) is an influential next-generationwireless communication system standard. In the LTE, when a base stationtransmits downlink data to a user equipment, the base station firsttransmits scheduling information on a downlink data channel through acontrol channel, allocates the downlink data channel according to thescheduling information, and transmits the downlink data through theallocated downlink data channel. The user equipment transmits to thebase station reception acknowledgement/non-acknowledgement (ACK/NACK) ofthe downlink data and the base station may transmit new downlink data orretransmit pretransmitted downlink data according to the ACK/NACK. Sucha data transmission scheme is called a hybrid automatic repeat request(HARQ). The HARQ includes synchronous and asynchronous HARQs, and in thecase of the synchronous HARQ, synchronization is set between an HARQprocess and a subframe, and as a result, new transmission/retransmissionof the same HARQ process is performed according to a predeterminedtiming. On the contrary, in the case of the asynchronous HARQ, the useof the HARQ is directly instructed without the synchronization betweenthe HARQ process and the subframe.

Meanwhile, 3GPP LTE-A (long term evolution-advanced) (hereinafter,referred to as LTE-A) is a next-generation wireless communication systemstandard developed by improving the LTE. The LTE-A can support lowprice/low specification user equipments that primarily perform datacommunications such as meter reading, water level measurement,utilization of a monitoring camera, inventory reporting of a vendingmachine, and the like. As described above, the low price/lowspecification user equipments that primarily perform low-capacity datacommunications are called a machine type communication (MTC) userequipment.

When the MTC user equipment exists in an area supported by the basestation, it may be difficult to apply the ACK/NACK timing of theexisting HARQ as it is. For example, when the downlink data has acapacity larger than a capacity which the MTC user equipment can processwithin a specific time, the MTC user equipment may not decode all of thedownlink data at the time of transmitting the ACK/NACK.

Further, in spite of not the MTC user equipment, data to beacknowledged/not acknowledged and a time up to the transmission timingof the ACK/NACK are insufficient, and as a result, an ACK/NACK responseof the HARQ may not normally be performed during a predetermined timeinterval.

For example, the LTE-A can support carrier aggregation and support crosscarrier scheduling. In the cross carrier scheduling, schedulinginformation is simultaneously received through a specific cell, but datascheduled by the scheduling information may be received in differentcells. In this case, the different cells are not temporally aligned, andas a result, data may be received lately in some cells. In this case,due to an insufficient time between the lately received data and aninsufficient time and an ACK/NACK thereof, the lately received data maynot normally be decoded.

Alternatively, in the LTE-A, a new control channel allocated to a datadomain may be introduced in addition to the existing control channelallocated to a control domain. Since the new control channel may existin the data domain, a decoding time of data scheduled by the new controlchannel may be insufficient according to the user equipment.

Therefore, new ACK/NACK transmitting method and apparatus which can beapplied to an advanced wireless communication system such as the LTE-Aare required.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and anapparatus for transmitting an ACK/NACK in a wireless communicationsystem.

In accordance with an aspect of the present invention, a method fortransmitting an acknowledgement/not-acknowledgement (ACK/NACK) of a userequipment includes the steps of: receiving a transport block; andtransmitting an ACK/NACK signal for the transport block in a firstsubframe or a second subframe according to the size of the transportblock, wherein, when the size of the transport block is equal to orsmaller than a preference value, the ACK/NACK signal is transmitted inthe first subframe and when the size of the transport block is largerthan the reference value, the ACK/NACK signal is transmitted in thesecond subframe, and the second subframe is behind the first subframe ina time domain.

In accordance with another aspect of the present invention, a method fortransmitting an acknowledgement/not-acknowledgement (ACK/NACK) of a userequipment includes the steps of: receiving a transport block; andtransmitting an ACK/NACK for the transport block in a predeterminedsubframe when the size of the transport block is larger than a referencevalue, and not transmitting the ACK/NACK for the transport block whenthe size of the transport block is equal to or smaller than thereference value.

In accordance with yet another aspect of the present invention, a userequipment includes: a radio frequency (RF) unit which transmits orreceives a radio signal; and a processor connected with the RF unit,wherein the processor receives a transport block and transmits anACK/NACK for the transport block in a first subframe or a secondsubframe according to the size of the transport block, and when the sizeof the transport block is equal to or smaller than a preference value,the ACK/NACK signal is transmitted in the first subframe and when thesize of the transport block is larger than the reference value, theACK/NACK signal is transmitted in the second subframe, and the secondsubframe is behind the first subframe in a time domain.

An HARQ process can be efficiently performed under a situation in whicha data decoding capability is limited. Accordingly, system performanceis improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a structure of an FDD radio frame.

FIG. 2 illustrates a structure of a TDD radio frame.

FIG. 3 illustrates one example of a resource grid for one downlink slot.

FIG. 4 illustrates a structure of a downlink subframe.

FIG. 5 illustrates a structure of an uplink subframe.

FIG. 6 illustrates a comparative example of a single carrier system anda carrier aggregation system.

FIG. 7 illustrates a channel coding process (channel coding chain) of atransport block.

FIG. 8 illustrates a method for transmitting an ACK/NACK of a userequipment according to an embodiment of the present invention.

FIG. 9 illustrates data receiving and ACK/NACK transmitting timings ofthe user equipment by the method of FIG. 8.

FIG. 10 illustrates a method for transmitting an ACK/NACK of a userequipment according to another embodiment of the present invention.

FIG. 11 illustrates a method for transmitting an ACK/NACK according tothe present invention.

FIG. 12 is a block diagram illustrating a wireless apparatus in whichthe embodiment of the present invention is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The user equipment (UE) may be fixed or movable and may be called otherterms such as a mobile station (MS), a mobile terminal (MT), a userterminal (UT), a subscriber station (SS), a wireless device, a personaldigital assistant (PDA), a wireless modem, a handheld device, and thelike.

The base station generally represents a fixed station that communicateswith the user equipment, and may be called other terms such as anevolved-NodeB (eNB), a base transceiver system (BTS), an access point,and the like.

A communication from the base station to the user equipment is called adownlink DL and a communication from the user equipment to the basestation is called an uplink UL. A wireless communication systemincluding the base station and the user equipment may be a time divisionduplex (TDD) or a frequency division duplex (FDD) system. The TDD systemis a wireless communication system that performs uplink and downlinktransmission and reception by using different timings in the samefrequency band. The FDD system is a wireless communication system thatcan perform the uplink and downlink transmission and receptionsimultaneously by using different frequency bands. The wirelesscommunication system may perform the communication by using the radioframe.

FIG. 1 illustrates a structure of an FDD radio frame.

The FDD radio frame includes 10 subframes and one subframe twoconsecutive slots. Slots included in the radio frames are indexed with 0to 19. A time required to transmit one subframe is a transmission timeinterval (TTI) and the TTI may be a minimum scheduling unit. Forexample, the length of one subframe may be 1 ms and the length of oneslot may be 0.5 ms.

FIG. 2 illustrates a structure of a TDD radio frame.

Referring to FIG. 2, a subframe having index #1 and index #6 is called aspecial subframe and includes a downlink pilot time slot (DwPTS), aguard period (GP), and an uplink pilot time slot (UpPTS). The DwPTS isused in initial cell search, synchronization, or channel estimation inthe user equipment. The UpPTS is used to match channel estimation in thebase station and uplink transmission synchronization of the userequipment. The GP is a period for removing an interference which occursin the uplink due to a multipath delay of the downlink signal betweenthe uplink and the downlink.

In the TDD, a downlink (DL) subframe and an uplink (UL) subframe coexistin one radio frame. Table 1 illustrates one example of a UL-DLconfiguration of the radio frame.

TABLE 1 Downlink- to-uplink Uplink- Switch- downlink point Subframe nconfiguration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  D S U U UD D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D D D D 6 5ms D S U U U D S U U D

In Table 1, ‘D’ represents a DL subframe, IT represents a UL subframe,and ‘S’ represents the special subframe. When the user equipmentreceives the UL-DL configuration from the base station, the userequipment may know whether each subframe is the DL subframe or the ULsubframe in the radio frame. Hereinafter, a UL-DL configuration N (N isany one of 0 to 6) may refer to Table 1.

FIG. 3 illustrates one example of a resource grid for one downlink slot.

Referring to FIG. 3, the downlink slot may include a plurality oforthogonal frequency division multiplexing (OFDM) symbols in a timedomain and N_(RB) resource blocks (RBs) in a frequency domain. Theresource block as the resource allocation unit includes one slot in thetime domain and a plurality of consecutive subcarriers in the frequencydomain. The number N_(RB) of resource blocks included in the downlinkslot is subordinate to a downlink bandwidth N^(DL) set in a cell. Forexample, in an LTE system, N_(RB) may be any one of 6 to 110. Astructure of an uplink slot may also be the same as that of the downlinkslot.

Each element on the resource grid is called a resource element (RE). Theresource element on the resource grid may be identified by a pair ofindexes (k,l) in the slot. Herein, k (k=0, . . . , N_(RB)×12-1)represents a subcarrier index in the frequency domain and l (l=0, . . ., 6) represents an OFDM symbol index in the time domain.

In FIG. 3, it is exemplarily described that one resource block isconstituted by 7 OFDM symbols in the time domain and 12 subcarriers inthe frequency domain and thus includes 7×12 resource elements, but thenumber of the OFDM symbols and the number of the subcarriers in theresource block are not limited thereto. The number of the OFDM symbolsand the number of the subcarriers may be variously changed depending onthe length of a CP, frequency spacing, and the like. As the number ofsubcarriers in one OFDM symbol, one may be selected and used among 128,256, 512, 1024, 1536, and 2048.

FIG. 4 illustrates a structure of a downlink subframe.

Referring to FIG. 4, the downlink (DL) subframe is divided into acontrol region and a data region. The control region includes maximumthree (maximum four in some cases) precedent OFDM symbols of a firstslot in the subframe, but the number of OFDM symbols included in thecontrol region may be changed. A physical downlink control channel(PDCCH) and other control channel are allocated to the control regionand a physical downlink shared channel (PDSCH) is allocated to the dataregion.

As disclosed in 3GPP TS 36.211 V8.7.0, a physical channel in 3GPP LTEmay be divided into the physical downlink shared channel (PDSCH) and aphysical uplink shared channel (PUSCH) which are data channels, and aphysical downlink control channel (PDCCH), a physical control formatindicator channel (PCFICH), a physical hybrid-ARQ indicator channel(PHICH), and a physical uplink control channel (PUCCH) which are datachannels.

The PCFICH transmitted in a first OFDM symbol of the subframe transportsa control format indicator regarding the number (that is, the size ofthe control region) of OFDM symbols used to transmit control channels inthe subframe. The user equipment first receives the CFI on the PCFICHand thereafter, monitors the PDCCH. Unlike the PDCCH, the PCFICH istransmitted through a fixed PCFICH resource of the subframe withoutusing blind decoding.

The PHICH transports a positive-acknowledgment(ACK)/negative-acknowledgement (NACK) signal for an uplink hybridautomatic repeat request (HARQ). An ACK/NACK signal for uplink (UL) dataon the PUSCH transmitted by the user equipment is transmitted on thePHICH.

A physical broadcast channel (PBCH) is transmitted in four precedentOFDM symbols of a second slot of the first subframe of the radio frame.The PBCH transports system information required for the user equipmentto communicate with the base station and the system informationtransmitted through the PBCH is called a master information block (MIB).As compared therewith, system information transmitted on the PDSCHinstructed by the PDCCH is called a system information block (SIB).

Control information transmitted through the PDCCH is called downlinkcontrol information (DCI). The DCI may include resource allocation (alsoreferred to as downlink (DL) grant) of the PDSCH, resource allocation(also referred to as uplink (UL) grant) of the PUSCH, a set oftransmission power control commands for individual UEs in apredetermined UE group, and/or activation of a voice over Internetprotocol (VoIP). Table 2 shown below exemplifies a DCI format and ausage.

TABLE 2 DCI format USAGE DCI FORMAT 0 USED IN SCHEDULING PUSCH DCIFORMAT 1 USED IN SCHEDULING ONE PDSCH CODWORD DCI FORMAT 1A USED INCOMPACT SCHEDULING OF ONE PDSCH CODEWORD AND RANDOM ACCESS PROCESS DCIFORMAT 1B USED IN COMPACT SCHEDULING OF ONE PDSCH CODEWORD HAVINGPRECODING INFORMATION DCI FORMAT 1C USED IN VERY COMPACT SCHEDULING OFONE PDSCH CODWORD DCI FORMAT 1D USED IN COMPACT SCHEDULING OF ONE PDSCHCODEWORD HAVING PRECODING AND POWER OFFSET INFORMATION DCI FORMAT 2 USEDIN SCHEDULING PDSCH OF USER EQUIPMENTS SET IN CLOSE LOOP SPATIALMULTIPLEXING MODE DCI FORMAT 2A USED IN SCHEDULING PDSCH OF USEREQUIPMENTS SET IN OPEN LOOP SPATIAL MULTIPLEXING MODE DCI FORMAT 3 USEDIN TRANSMITTING TPC COMMAND OF PUCCH AND PUSCH HAVING 2 BIT POWERADJUSTMENTS DCI FORMAT 3A USED IN TRANSMITTING TPC COMMAND OF PUCCH ANDPUSCH HAVING 1 BIT POWER ADJUSTMENT DCI FORMAT 4 USED IN SCHEDULINGPUSCH IN ONE UL CELL IN MULTI ANTENNA TRANSMISSION MODE

FIG. 5 illustrates a structure of an uplink subframe.

Referring to FIG. 5, the uplink subframe may be divided into a controlregion to which the physical uplink control channel (PUCCH) transportingthe uplink control information is allocated and a data region to whichthe physical uplink shared channel (PUSCH) transporting user data isallocated, in the frequency domain.

The PUCCH is allocated as a pair of RBs in the subframe. The RBs thatbelong to the pair of RBs occupy different subcarriers in first andsecond slots, respectively. The pair of RBs have the same resource blockindex m.

According to the 3GPP TS 36.211 V8.7.0, the PUCCH supports multipleformats. PUCCH having different bit numbers for each subframe may beused according to a modulation scheme subordinate to the PUCCH format.

PUCCH format 1 is used to transmit a scheduling request (SR), PUCCHformat 1a/1b is used to transmit the ACK/NACK signal for the HARQ, PUCCHformat 2 is used to transmit a CQI, and PUCCH format 2a/2b is used tosimultaneously transmit the CQI and the ACK/NACK signal. PUCCH format 3may be used to transmit a plurality of ACKs/NACKs.

In the 3GPP LTE, a resource index n⁽¹⁾ _(PUCCH) is defined in order forthe user equipment to configure the PUCCH. The resource index is definedas n⁽¹⁾ _(PUCCH)=n_(CCE)+N⁽¹⁾ _(PUCCH), n_(CCE) is No. of a first CCEused to transmit the corresponding PDCCH (that is, PDCCH includingdownlink resource allocation used to receive the downlink datacorresponding to the ACK/NACK signal), and N⁽¹⁾ _(PUCCH) is a parameterwhich the base station notifies to the user equipment as a higher layermessage.

The resource that transmits the ACK/NACK may be instructed by the n⁽¹⁾_(PUCCH) and in this case, implicit mapping of the CCE and the ACK/NACKresource is used.

Hereinafter, a carrier aggregation system will be described. The carrieraggregation system is also referred to as a multiple carrier system or amultiple cell system.

The 3GPP LTE system supports a case in which a downlink bandwidth and anuplink bandwidth are set to be different from each other, but thispremises one component carrier (CC). The 3GPP LTE system supportsmaximum 20 MHz and the uplink bandwidth and the downlink bandwidth maybe different from each other, but the 3GPP LTE system supports only oneCC to each of the uplink and the downlink.

On the contrary, carrier aggregation supports a plurality of CCs. Forexample, when five CCs are allocated as granularity of the unit of thecarrier having a bandwidth of 20 MHz, a bandwidth of maximum 100 MHz maybe supported.

One DL CC or a pair of UL CC and DL CC may correspond to one cell.Therefore, the user equipment that communicates with the base stationthrough a plurality of DL CCs may receive a service from a plurality ofserving cells.

FIG. 6 illustrates a comparative example of a single carrier system anda carrier aggregation system.

A carrier aggregation system (FIG. 6(b)) has each of three DL CCs and ULCCs, but the numbers of DL CCs and UL CCs are not limited. In each DLCC, the PDCCH and the PDSCH may be independently transmitted and in eachUL CC, the PUCCH and the PUSCH may be independently transmitted.Alternatively, the PUCCH may be transmitted through only a specific ULCC.

Since three pairs of the DL CC and the UL CC are defined, the userequipment may receive the service from three serving cells.

The user equipment may monitor the PDCCH in the plurality of DL CCs andreceive a DL transport block simultaneously through the plurality of DLCCs. The user equipment may transmit a plurality of UL transport blockssimultaneously through a plurality of UL CCs.

A pair of DL CC #A and UL CC #A may become a first serving cell, a pairof DL CC #B and UL CC #B may become a second serving cell, and a pair ofDL CC #C and UL CC #C may become a third serving cell. Each serving cellmay be identified through a cell index (CI). The CI may be unique in thecell or user equipment-specific.

The serving cell may be divided into a primary cell (PCell) and asecondary cell (SCell). The primary cell is a cell designated as theprimary cell while the user equipment performs an initial connectionestablishment process or starts a connection reestablishment process, orduring a handover process. The primary cell is also referred to as areference cell. The secondary cell may be set after an RRC connection isestablished and may be used to provide an additional radio resource. Atleast one primary cell may be continuously set and the secondary cellmay be add/modified/cancelled by higher layer signaling (e.g., an RRCmessage). A CI of the primary cell may be fixed. For example, a lowestCI may be designated as the CI of the primary cell.

The primary cell is constituted by a downlink primary component carrier(DL PCC) and an uplink primary component carrier (UL PCC) in terms of acomponent carrier. The secondary cell may be constituted by only adownlink secondary component carrier or a pair of the DL SCC and anuplink secondary component carrier (UL SCC), in terms of the componentcarrier.

Hereinafter, ACK/NACK transmission for the HARQ in 3GPP LTE timedivision duplex (TDD) will be described.

In the TDD, the DL subframe and the UL subframe coexist in one radioframe unlike frequency division duplex (FDD). In general, the number ofUL subframes is smaller than the number of DL subframes. Accordingly,against insufficient UL subframes for transmitting the ACK/NACK signal,it is supported that a plurality of ACK/NACK signals for downlink data(that is, DL transport blocks) received in the plurality of DL subframesis transmitted in one UL subframe.

In a table shown below, a DL subframe n-k associated with a UL subframen depending on the UL-DL configuration, herein, k∈K, M represents thenumber of components of a set K.

TABLE 3 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 — — 6 — 4 —— 6 — 4 1 — — 7, 6 4 — — — 7, 6 4 — 2 — — 8, 7, 4, 6 — — — — 8, 7, 4, 6— — 3 — — 7, 6, 11 6, 5 5, 4 — — — — — 4 — — 12, 8, 7, 11 6, 5, 4, 7 — —— — — — 5 — — 13, 12, 9, 8, 7, 5, 4, 11, 6 — — — — — — — 6 — — 7 7 5 — —7 7 —

If an ACK/NACK for data (for example, a downlink data channel (transportblock) or a control channel requiring the ACK/NACK) received in the DLsubframe n is transmitted in a UL subframe n+k(n), the k(n) may beexpressed as shown in the following table.

TABLE 4 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 4 6 — 4 6 —1 7 6 4 7 6 4 2 7 6 4 8 7 6 4 8 3 4 11  7 6 6 5 5 4 12  11  8 7 7 6 5 45 12  11  9 8 7 6 5 4 13  6 7 7 7 7 5

In Table 4, when the user equipment receives the PDSCH or the PDCCH (forexample, a DL SPS cancellation PDCCH) requiring the ACK/NACK response,the ACK/NACK is transmitted in the subframe n+k(n) and respective valuesof Table 4 represent the k(n) value. For example, in the case where theUL-DL configuration is 0, when the PDSCH is received in subframe 0, theACK/NACK is transmitted in subframe 4 after four subframes. The userequipment requires a specific time in order to transmit the ACK/NACKafter receiving the PDSCH or the DL SPS cancellation PDCCH. Hereinafter,a minimum value of the specific time is expressed as k_(min) and a valuethereof may be four subframes. In Table 4, referring to the time oftransmitting the ACK/NACK, it may be known that the ACK/NACK may bemostly transmitted in an initial uplink subframe in which k_(min) haselapsed. However, a numerical figure underlined in Table 4 does notindicate the initial uplink subframe in which k_(min) has elapsed andindicates an uplink subframe positioned next thereto. The reason is toprevent the ACK/NACK from being transmitted to too many downlinksubframes in one uplink subframe.

Hereinafter, the size of the transport block (TB) and a channel codingprocess in the LTE will be described.

First, the size of the transport block is determined according toI_(TBS) and N_(PRB) as shown in Table 5. However, N_(PRB) may have apredetermined value of 1 to 110 and represents only up to 10 in Table 5.

TABLE 5 N_(PRB) I_(TBS) 1 2 3 4 5 6 7 8 9 10 0 16 32 56 88 120 152 176208 224 256 1 24 56 88 144 176 208 224 256 328 344 2 32 72 144 176 208256 296 328 376 424 3 40 104 176 208 256 328 392 440 504 568 4 56 120208 256 328 408 488 552 632 696 5 72 144 224 328 424 504 600 680 776 8726 328 176 256 392 504 600 712 808 936 1032 7 104 224 328 472 584 712 840968 1096 1224 8 120 256 392 536 680 808 968 1096 1256 1384 9 136 296 456616 776 936 1096 1256 1416 1544 10 144 328 504 680 872 1032 1224 13841544 1736 11 176 376 584 776 1000 1192 1384 1608 1800 2024 12 208 440680 904 1128 1352 1608 1800 2024 2280 13 224 488 744 1000 1256 1544 18002024 2280 2536 14 256 552 840 1128 1416 1736 1992 2280 2600 2856 15 280600 904 1224 1544 1800 2152 2472 2728 3112 16 328 632 968 1288 1608 19282280 2600 2984 3240 17 336 696 1064 1416 1800 2152 2536 2856 3240 362418 376 776 1160 1544 1992 2344 2792 3112 3624 4008 19 408 840 1288 17362152 2600 2984 3496 3880 4264 20 440 904 1384 1864 2344 2792 3240 37524136 4584 21 488 1000 1480 1992 2472 2984 3496 4008 4584 4968 22 5201064 1608 2152 2664 3240 3752 4264 4776 5352 23 552 1128 1736 2280 28563496 4008 4584 5160 5736 24 584 1192 1800 2408 2984 3624 4264 4968 55445992 25 616 1256 1864 2536 3112 3752 4392 5160 5736 6200 26 712 14802216 2984 3752 4392 5160 5992 6712 7480

The transport block is channel-coded.

FIG. 7 illustrates a channel coding process (channel coding chain) of atransport block.

Referring to FIG. 7, a cyclic redundancy check (CRC) is added to thetransport block (TB) (S701), which becomes a code block (CB). When thesize of the transport block is represented by A and the size of the CRCis represented by L, B (=A+L) which is a sum of the A and the L iscompared with Z (=6144 bits) and when B is equal to or larger than Z,code block segmentation is performed (S702). The CRC is added for eachdivided code block (S703) and the transport block is channel-coded(S704). As the channel coding, turbo encoding may be used. The dividedcode block added with the CRC becomes 6144 bits or less. Thereafter, thecode block is subjected to rate matching (S705) and code blockconcatenation (S706).

Hereinafter, the present invention will be described.

The LTE-A may support low price/low specification terminals thatprimarily perform data communications. For example, meter reading, waterlevel measurement, utilization of a monitoring camera, inventoryreporting of a vending machine, and the like are primarily performed bythe data communications and the data communications are sufficientlyperformed by even the low price/low specification user equipment. TheLTE-A may support the user equipment. Hereinafter, the low price/lowspecification user equipment is called a machine type communication(MTC) user equipment.

In the case of the MTC user equipment, it may be important tosimply/minimize a radio frequency (RF) chain or a channel coding chainin order to reduce manufacturing cost of the user equipment.

In the case of the downlink data channel that operates by the HARQprocess, the ACK/NACK response representing whether to normally receivethe data by processing the received data is transmitted. In this case,in the HARQ process, a time required to transmit the ACK/NACK responseis predetermined. For example, in the case of the LTD FDD, the ACK/NACKis transmitted in a subframe after four subframes in the subframereceiving the PDSCH. In the case of the LTE TDD, the subframe thattransmits the ACK/NACK may vary according to the UL/DL configuration foreach subframe, but the ACK/NACK is transmitted in the subframe afterminimum four subframes in the subframe receiving the PDSCH (this hasalready been described).

Regardless of the FDD or the TDD, the user equipment decodes thedownlink data (that is, the transport block) within a predetermined timeand needs to generate/transmit the ACK/NACK therefor. If the size of thetransport block is larger than a predetermined value, the user equipmentwill allocate a plurality of channel coding chains to the transportblock and parallelize the transport block in order to decode thetransport block within a predetermined time or adjust a processingcapability by increasing a clock speed. However, in the case of the MTCuser equipment, it is not preferable to set the processing capability tosupport the maximum transport block size within a predetermined timewhen an increase of the manufacturing cost, a low use frequency of thetransport block having the maximum size, and the like are considered.

Hereinafter, a method for transmitting an ACK/NACK will be described,for a user equipment of which a decoding capability is limited, such asthe MTC user equipment. Further, a method for transmitting and receivingdata between the user equipment of which the decoding capability islimited, such as the MTC user equipment and the base station will bedescribed. Hereinafter, the user equipment means the user equipment ofwhich the decoding capability is limited, such as the MTC userequipment, but in the present invention, the user equipment is notlimited thereto. That is, the present invention may be applied to even ageneral LTE/LTE-A user equipment.

FIG. 8 illustrates a method for transmitting an ACK/NACK of a terminalaccording to an embodiment of the present invention.

Referring to FIG. 8, the user equipment judges whether the size of thetransport block is larger than a predetermined value (S110).Hereinafter, it will be assumed that the predetermined value is X. X maybe 1) the maximum size of the transport block in an initial access andan initial configuration. That is, it may not be known whether the userequipment is the existing user equipment or the MTD user equipment ofwhich the decoding capability is limited in the initial access or theinitial RRC configuration. Accordingly, the maximum size of thetransport block in the initial access and the initial RRC configurationmay be set to X for counter compatibility. As a result, the existingHARQ timing may be maintained in the initial access and the initial RRCconfiguration.

Alternatively, X may be determined 2) by considering code blocksegmentation and a code block processing capability of the MTD userequipment. For example, if the block processing capability of the MTCuser equipment is one code block, X=Z−L=6144−24=6120 (bits). If theblock processing capability of the MTC user equipment is two, X becomes2*6120 (bits).

If the size of the transport block is equal to or smaller than apredetermined value, the ACK/NACK for the transport block is transmittedin the first subframe (S120). Herein, the first subframe may be asubframe at a minimum ACK/NACK transmittable timing or the existingACK/NACK transmission subframe. In this sense, the first subframe may becalled a default subframe. For example, in the LTE 1-DD, when thetransport block is received in subframe N, an ACK/NACK for the transportblock is transmitted in subframe N+4. In this case, the subframe N+4becomes the first subframe.

More generally, if subframes are consecutively indexed in an ascendingorder (if a last subframe of a frame is i, a first subframe of a nextframe is represented by i+1), when a data unit (data to beacknowledged/not acknowledged, such as the PDSCH, the transport block,or the like) is received, the ACK/NACK for the data channel istransmitted in subframe n+k_(default). In this case, the first subframebecomes the subframe n+k_(default) based on the subframe n. In the FDD,k_(default) may be 4 and in the TDD, k_(default) may be a value of Table4.

If the size of the transport block is larger than the predeterminedvalue, the ACK/NACK for the transport block is transmitted in the secondsubframe (S130).

The second subframe as the subframe in which the ACK/NACK is transmittedwhen the size of the transport block is larger than a predeterminedvalue is a subframe temporally later than the first subframe. Forexample, the data unit (data to be acknowledged/not acknowledged, suchas the PDSCH, the transport block, or the like) is received in thesubframe n and when the size of the data unit is larger than thepredetermined value, the ACK/NACK for the data unit is transmitted insubframe n+k_(default)+k_(add)(k_(add)>0).

Alternatively, a method for suspending (stopping) the ACK/NACKtransmission may be used. This shows the same effect as setting kadd toinfinity and the base station performs scheduling by arbitrarily judgingretransmission/new retransmission without the ACK/NACK response.Suspending (stopping) the ACK/NACK transmission as described above maybe applied to a case in which the data unit does not reach apredetermined value. The reason is that loss may be small even thoughdata having a small amount is arbitrarily retransmitted or thecorresponding data is lost without the ACK/NACK response.

As the k_(add), a value set by a higher layer signal such as a radioresource control (RRC) message may be used. Alternatively, as k_(add), apredetermined specific value (for example, any value of 1, 2, 3, and 4and this just an example) may be used. k_(add) may be determined byconsidering the number of code blocks, the size of the transport block,and the like.

In the case of the TDD, an HARQ ACK time delay, that is, k(n) may be setto be larger than k_(default) according to subframe No. n as shown inTable 4. In this case, when k(n) is equal to or larger thank_(default)+k_(add), k(n) is followed. That is, a value of min(k(n),k_(default)+k_(add)) may be used the HARQ ACK time delay. Herein,min(x,y) represents a smaller value (the same value if x and y are thesame as each other) of x and y.

Alternatively, k(n) may be limited to schedule a transport block largerthan predetermined X only in downlink subframe n in which k(n) is equalto or larger than k_(default)+k_(add).

In FIG. 8, an example of directly comparing whether the size of thetransport block is larger than the predetermined value X is described,but the present invention is not limited thereto. For example, it may bedetermined which subframe of the first and second subframes the ACK/NACKis transmitted based on specific I_(TBS) and N_(PRB) of Table 5 insteadof X. For example, I_(TBS) has any value of 0 to 26 and N_(PRB) has anyvalue of 1 to 10, and the size of the transport block is determinedaccording to I_(TBS) and N_(PRB). Therefore, the size of the transportblock may be instructed by I_(TBS) and N_(PRB). Accordingly, sectionsfor I_(TBS) and N_(PRB) are divided and thereafter, whether the ACK/NACKis transmitted in the first subframe or the second subframe may bediscriminated based on a specific section or a specific value.

FIG. 9 illustrates data receiving and ACK/NACK transmitting timings ofthe user equipment by the method of FIG. 8.

Referring to FIG. 9, the user equipment may receive a PDSCH 901 in whichthe size of the transport block is equal to or smaller than X and aPDSCH 902 in which the size of the transport block is larger than X insubframe n.

The user equipment transmits an ACK/NACK for the PDSCH 901 in subframen+k_(default) and transmits an ACK/NACK for the PDSCH 902 in subframen+k_(default)+k_(add).

FIG. 10 illustrates a method for transmitting an ACK/NACK of a userequipment according to another embodiment of the present invention.

Referring to FIG. 10, the user equipment judges whether a DCI format toschedule the PDSCH is a predetermined specific DCI format (S210).

For example, DCI format 1A is called a fallback DCI format as a DCIformat which is continuously supported regardless of a downlinktransmission mode. The user equipment judges whether the DCI formatdetected in the PDCCH region is the fallback DCI format and if thedetected DCI format is the fallback DCI format, the ACK/NACK for thetransport block scheduled by the DCI format is transmitted in the firstsubframe (S220) and if not so, the ACK/NACK for the transport blockscheduled by the DCI format is transmitted in the second subframe(S230).

The size of the transport block scheduled by the fallback DCI format maybe limited by a scheduler according to a processing capability of theuser equipment.

The present invention in which the transmission timing of the ACK/NACKmay be differently applied according to a condition of the size of thedata unit to be acknowledged/non acknowledged may be variously extendedas described below.

For example, the subframe in which the ACK/NACK is transmitted may bedivided according to search space in which the DCI is transmitted. Forexample, different ACK/NACK transmission timings may be applied byconsidering which space of a common search space (CSS) which is a commonsearch space for all user equipments in a cell and a user equipmentspecific search space (USS) which is a search space for a specific userequipment the DCI is received from.

Alternatively, different ACK/NACK transmission timings may be applied byconsidering whether being scheduled by the PDCCH or an E-PDCCH(enhanced-PDCCH, described below).

Alternatively, different transmission timings may be applied accordingto a subframe (alternatively, a cell) in which scheduling DCI istransmitted, different transmission timings may be applied according toa subframe (alternatively, a cell) in which a scheduled data channel istransmitted, different transmission timings may be applied according towhether a scheduling scheme being semi-persistent scheduling (SPS) (forexample, a PDSCH without a corresponding PDCCH) or dynamic (a PDSCH withthe corresponding PDCCH), different transmission timings may be appliedaccording to a type of a radio network temporary identifier (RNTI) addedto the DCI, or different transmission timings may be applied accordingto cross scheduling or non-cross scheduling.

FIG. 11 illustrates a method for transmitting an ACK/NACK according tothe present invention.

Referring to FIG. 11, the user equipment receives the RRC message forsetting X and k_(add) through the RRC message (S310).

The user equipment receives the transport block through the PDSCH of thesubframe n (S320).

The user equipment compares the size of the transport block with X(S330), transmits the ACK/NACK in the subframe n+k_(default) when thesize of the transport block is equal to or smaller than X (S340-1), andtransmits the ACK/NACK in the subframe n+k_(default)+k_(add) when thesize of the transport block is larger than X (S340-2).

In FIG. 11, a case in which both X and k_(add) are (directly orindirectly) set by the RRC message is exemplified for easy description.However, the present invention is not limited thereto and only one of Xand k_(add) may be set by one RRC message. In this case, as a value notset by the RRC message, a predetermined value may be used between theuser equipment and the base station. Further, the base station maysignal k_(default)+k_(add) by the RRC message instead of k_(add).Alternatively, both X and k_(add) are not RRC-signaled and may bepredetermined values.

Meanwhile, the base station may transmit information on the ACK/NACKtransmission timing included in the DCI. For example, information onk_(add) may be signaled by configuring a specific field in the DCI orcombining states of other fields. That is, the base station may instructthe second subframe to the user equipment through the DCI.

Alternatively, an instructor that disables the ACK/NACK to betransmitted may also be included in the DCI. The user equipment does nottransmit the ACK/NACK when it is judged that the ACK/NACK is instructednot to be transmitted through the instructor. The instructor may beincluded separately from the specific field of the DCI. Alternatively,in the case of the instructor, a value of the specific field itself mayserve as the instructor. For example, when the specific field is 2 bitsand states of the specific field are ‘00’, ‘01’, ‘10’, and ‘11’ and‘00’, ‘01’, and ‘10’ may sequentially represent that k_(add) is 0, 1,and 2 and ‘11’ may represent that k_(add) is infinite and thus theACK/NACK is not transmitted.

In the above, when the size of the transport block is larger than aspecific value X, a positive k_(add) value is added as an example, butthe present invention is not limited thereto. That is, k_(add) may havea negative value. Alternatively, k_(minus) may be signaled separatelyfrom k_(add). For example, when k_(default) is set sufficiently,k_(minus) may be subtracted.

Hereinafter, the resource allocation in the subframe in which theACK/NACK is transmitted will be described.

In the FDD, when the ACK/NACK is transmitted, the resource allocationmay be performed as follows.

1. When k_(default) is applied (that is, when the ACK/NACK for the dataunit received in the subframe n is transmitted in the subframen+k_(default), hereinafter, the same as above), the ACK/NACK may betransmitted by using an implicit resource. That is, the resource thattransmits the ACK/NACK may be determined based on a lowest CCE of thePDCCH that schedules the transport block to be acknowledged/notacknowledged.

2. When k_(default)+k_(add) is applied (that is, when the ACK/NACK forthe data unit received in the subframe n is transmitted in the subframen+k_(default)+k_(add), hereinafter, the same as above), the ACK/NACK maybe transmitted by using an explicit resource set by the RRC. When theimplicit resource is used in the case where k_(default)+k_(add) isapplied, mapping of the CCE and the ACK/NACK resource different from theimplicit resource determined in Clause 1 may be set.

In the TDD, when the ACK/NACK is transmitted, the resource allocationmay be performed as follows.

1. When k(n) is applied, the ACK/NACK may be transmitted by using theimplicit resource.

2. When k_(default)+k_(add) is applied (for example, when k(n) of Table4 is smaller than k_(default)+k_(add)), the ACK/NACK may be transmittedby using the explicit resource set by the RRC. When the implicitresource is used in the case where k_(default)+k_(add) is applied,mapping of the CCE and the ACK/NACK resource different from the implicitresource determined in k(n) may be set.

Meanwhile, the present invention may be applied even to the carrieraggregation system. That is, the present invention may be applied whenmultiple cells are set for the user equipment. Reception timings of thePDSCH are different for each of multiple cells (alternatively, for eachcell group) set for the user equipment, and as a result, multiple timingalignments (TAs) may be applied. In this case, when a specific cellbecomes a monitoring cell and cross carrier scheduling is appliedbetween the cells, the reception timings of the PDCCH are the same aseach other, but the reception timings of the PDSCH may be different fromeach other in respective cells.

For example, cells #1, 2 and 3 are set for the user equipment and thecross carrier scheduling is set, and as a result, the PDCCHs may bereceived through subframe #n of the cell #1. In this case, framesynchronization is not matched among the cells #1, 2, and 3, and as aresult, the TA may be performed and then, the PDSCHs in the cells #1, 2,and 3 may be received different timings. In this case, a decoding timeof the PDSCH received late may be insufficient. If the ACK/NACKs for thePDSCHs received in the cells #1, 2, and 3 need to be transmitted in theuplink subframe of one cell (for example, the primary cell), a problemmay occur due to the insufficient decoding time for the PDSCH receivedlate.

In this case, the ACK/NACK for the PDSCH received late may betransmitted in not the subframe #n+k_(default) but the subframe#n+k_(default)+k_(add) by modifying and applying the present invention.

Further, the present invention may be applied even to a wirelesscommunication system including the enhanced-PDCCH (E-PDCCH). Herein, theE-PDCCH is a control channel included in the data region in a subframeincluding the control region and the data region, and may be a controlchannel decoded through a common reference signal (CRS) common to alluser equipments in the cell and a user equipment-specific referencesignal.

The case of scheduling the PDSCH by the PDCCH and the case of schedulingthe PDSCH by the E-PDCCH may be different from each other in a decodingstart time of the PDSCH. A decoding ability may be insufficientaccording to the user equipment in the case of scheduling the PDSCH bysetting the E-PDCCH. Even in this case, the present invention may bemodified and applied. For example, in the case of scheduling the PDSCHof the subframe n by the PDCCH of the subframe n, the ACK/NACK for thePDSCH may be transmitted in the subframe n+k_(default). In addition, inthe case of scheduling the PDSCH of the subframe n by the E-PDCCH of thesubframe n, the ACK/NACK for the PDSCH may be transmitted in thesubframe n k_(default)+k_(add). In this case, k_(add) may be determinedaccording to an amount in which the PDSCH decoding time is decreased interms of the user equipment.

In the aforementioned methods, a method for controlling an HARQ ACK/NACKtiming according to the size of the transport block has been described.

Meanwhile, according to yet another embodiment of the present invention,the user equipment may not transmit the ACK/NACK for the transport blockaccording to the size of the transport block. That is, when the size ofthe transport block is larger than predetermined X bits, the ACK/NACK istransmitted only when the size of the transport block is equal to orsmaller than the X without transmitting the ACK/NACK. This method is notlimited to a case based on the size of the transport block and thismethod includes a method in which the ACK/NACK is not transmitted whenthe size of the transport block is larger than a predetermined referencebased on the DCI format, I_(TBS) and N_(PRB), and the like.

FIG. 12 is a block diagram illustrating a wireless apparatus in whichthe embodiment of the present invention is implemented.

The base station 100 includes a processor 110, a memory 120, and a radiofrequency (RF) unit 130. The processor 110 implements a proposedfunction, a proposed process, and/or a proposed method. For example, theprocessor 110 transmits a downlink grant to the user equipment andtransmits downlink data such as the transport block through the radioresource allocated through the downlink grant. A subframe that receivesthe ACK/NACK may be determined according to the size of the transportblock. Further, the processor 110 may transmit the reference value X andk_(add) (alternatively, k_(default)+k_(add)) through the higher layersignal such as the RRC message. Further, the processor 110 may determinethe subframe that receives the ACK/NACK according to the DCI format. Thememory 120 is connected with the processor 110 to store various piecesof information for driving the processor 110. The RF unit 130 isconnected with the processor 110 to transmit and/or receive a radiosignal.

The user equipment 200 includes a processor 210, a memory 220, and an RFunit 230. The processor 210 implements a proposed function, a proposedprocess, and/or a proposed method. For example, the processor 210 mayreceive the transport block and transmit the ACK/NACK for the transportblock by using the subframe determined according to the size of thetransport block. The process of determining the subframe has beendescribed with reference to FIGS. 8 and 9. Further, the processor 210may determine the subframe to transmit the ACK/NACK according to the DCIformat. This process has been described with reference to FIG. 10.Further, the processor 210 may receive the reference value X and k_(add)(alternatively, k_(default)+k_(add)) through the higher layer signalsuch as the RRC message and use the received reference value X andk_(add) (alternatively, k_(default)+k_(add)). The memory 220 isconnected with the processor 210 to store various pieces of informationfor driving the processor 210. The RF unit 230 is connected with theprocessor 210 to transmit and/or receive a radio signal.

The processors 110 and 210 may include an application-specificintegrated circuit (ASIC), other chipset, a logic circuit, a dataprocessing device, and/or a converter that converts a baseband signaland a radio signal to each other. The memories 120 and 220 may include aread-only memory (ROM), a random access memory (RAM0, a flash memory, amemory card, a storage medium, and/or other storage device. The RF units130 and 230 may include one or more antennas that transmit and/orreceive the radio signal. When the embodiment is implemented bysoftware, the aforementioned technique may be implemented by a module (aprocess, a function, and the like) that perform the aforementionedfunction. The module may be stored in the memories 120 and 220 and maybe executed by the processors 110 and 210. The memories 120 and 220 maybe present inside or outside the processors 110 and 210 and connectedwith the processors 110 and 210 by various well-known means.

1-11. (canceled)
 12. A method for transmittingacknowledgement/not-acknowledgement (ACK/NACK) information, the methodperformed by a user equipment (UE) and comprising: receiving datascheduled by downlink control information (DCI) in a subframe n; andtransmitting ACK/NACK information for the data in a subframe n+k_(add),wherein each of the n and the k_(add) is an integer, and wherein a valueof k_(add) depends on the DCI.
 13. The method of claim 12, wherein thevalue of k_(add) is a natural number larger than
 4. 14. The method ofclaim 12, wherein the DCI includes a field informing the value ofk_(add).
 15. The method of claim 12, wherein the value of k_(add) islarger than
 4. 16. The method of claim 12, wherein the UE uses afrequency division duplex (FDD) frame.
 17. A user equipment (UE),comprising: a transceiver which transmits or receives a radio signal;and a processor connected with the transceiver, wherein the processorreceives data scheduled by downlink control information (DCI) in asubframe n, and transmis ACK/NACK information for the data in a subframen+k_(add), wherein each of the n and the k_(add) is an integer, andwherein a value of k_(add) depends on the DCI.
 18. The UE of claim 17,wherein the value of k_(add) is a natural number larger than
 4. 19. TheUE of claim 17, wherein the DCI includes a field informing the value ofk_(add).
 20. The UE of claim 17, wherein the value of k_(add) is largerthan
 4. 21. The UE of claim 17, wherein the UE uses a frequency divisionduplex (FDD) frame.